For many years for limiting the temperature and for energy conservation, thermostats have had means to limit the adjustment of a temperature control point adjusting means or lever to some selected value for both heating and cooling operations. In thermostats making use of separate adjusting levers for heating and/or cooling, the limiting action is quite simple in that a stop is used for the heating lever and a stop is used for a cooling lever and these stops can be independently adjusted.
In thermostats such as the Walter E. Edelman et al U.S. Pat. No. Re. 28,676, issued Jan. 13, 1976, having a single temperature control point adjustment means for both the heating and cooling operation, stops for both heating and cooling operation are difficult to use in that there are two ranges of operation for the heating and/or cooling apparatus. One particular method of accomplishing the limiting action is shown in the Donald P. Kolbow U.S. Pat. No. 4,078,601, issued Mar. 14, 1978. The thermostat has a single temperature control point adjustment means with separate ranges for the heating and cooling operation and a changeover switch which provides an off operation between the two ranges. With such a thermostat, a heating operation can be accomplished to limit the maximum heating temperture and a cooling operation can be selected to limit the minimum cooling temperature. Such a thermostat has certain disadvantages, one of which is that the thermostat temperature control point adjustment means can be inadvertently placed in the off position and the homeowner would not be aware that the system was completely off.
The present invention is concerned with a thermostat having a changeover switch means which selects the limiting action of the thermostat depending upon whether the thermostat is in the heating or cooling operation so that during the heating operation a first range of operation is selected and during the cooling operation a second range of operation is selected. With such an invention, the ranges can be set to provide for a maximum temperature during the heating operation of 72.degree. and a minimum temperature of 78.degree. for the cooling operation by the changeover operator. The temperature selection is made by the single temperature control point adjusting means or knob.